The aim of this study was to investigate factors associated with double contour formation (DCF) in mandibular condyle by comparing magnetic resonance (MR) images obtained before and after splint therapy. Disk position, cortical bone status of condyle, and joint fluid were evaluated for 6 temporomandibular joints (5 patients) with DCF. For comparison, the remaining 4 joints without DCF were also included in the evaluation. All of the 6 joints with DCF showed the anterior disk displacement before therapy while the 4 joints without DCF showed the normal disk position. After therapy, the disk position of all joints with DCF was improved. Two joints with DCF showed cortical erosion before therapy and their erosive changes disappeared after therapy. Four joints with DCF showed large joint effusion before therapy and they disappeared or diminished after therapy. According to these results, it can be concluded that double contour formation is associated with improvement of disk position and joint fluid.

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Objectives: Recently, many authors have tested the performance of the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD). The RDC/TMD have been translated into 18 languages and are being used by a consortium of RDC/TMD-based international researchers. We set out to validate the Grading of Severity of Chronic Pain (GSCP) in RDC/TMD for Japanese patients with TMD.
Methods: We used the GSCP in the Japanese version of RDC/TMD. Four hundred and forty-eight patients out of a total of 542 patients with TMD were analyzed. The GSCP included 7 questions on 3 items: Characteristic Pain Intensity (item 1, three questions), Disability score (item 2, three questions), and Disability days (item 3, one question). To assess cross-validity of the GSCP, patients were split randomly into two groups of roughly the same size (groups 1 and 2). We used three statistical methods to check the validation: the Mokken analysis method for cross-validity, structural equation modeling (SEM) for factor-validity, and the Spearman correlation coefficient for criterion based validity.
Results: Using the Mokken scale analysis, the item coefficient H (item H) level for group 1 showed a range of 0.64≤item H≤0.72 (0.43≤item H≤0.62 for group 2), and the scale coefficient H (H) was 0.70 and 0.57 for each group, respectively. The results indicated monotone homogeneity. Furthermore, reliability of the scales of groups 1 and 2 were 0.83 and 0.77, respectively, indicating double monotonicity. SEM yielded a substantially excellent model fit. GSCP showed a criterion based validity with a visual analog scale and a questionnaire to assess pain-related limitations of daily functions.
Conclusion: In this series of Japanese TMD patients, cross-validity, factor validity, and criterion based validity of GSCP were demonstrated, and the GSCP subscales were used to compare Japanese and English speaking patients with TMD.

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